Well, it's possible you could have an image where you see the impact of a snowball, but not any actual snowballs. In that case, I think the snowball tag wouldn't really fit but it's still a snowball fight.
Its weird, I commented in this thread but my reply is gone.
There are already cases tagged snowball that show the impact. In this case, I don't think we need to be so specific that including an image of the snowball impacting doesn't apply.
